1. Field of the Invention
The present invention relates to a display device using a thin film transistor at least in a pixel portion and a method for manufacturing the display device, and specifically relates to a display device having a pixel portion with a high aperture ratio and a method for manufacturing the display device.
2. Description of the Related Art
In recent years, a large liquid crystal module with a diagonal of greater than or equal to 30 inches or 40 inches has been actively developed for use as display devices such as liquid crystal televisions. In particular, demand for high definition panels for full high-definition (FHD) television or the like is high. A variety of characteristics such as high speed response corresponding to a speed of displaying a moving picture, excellent color reproducibility, sufficient luminance, and a high viewing angle in addition to high definition described above are needed especially in a liquid crystal module for use as liquid crystal televisions.
Conventionally, as the liquid crystal module for liquid crystal televisions, an active matrix module in which a plurality of pixels each having a thin film transistor (hereinafter, referred to as a TFT) using amorphous silicon as an active element are arranged has been used. In particular, the TFT generally has an inversed staggered structure which is suitable for mass production. In an element substrate having such an inversed staggered amorphous silicon TFT, a conductive film which is first deposited over the substrate (hereinafter, referred to as a first conductive film) has been used as a scan signal line (also referred to as a gate wiring), and a conductive film which is formed over a gate insulating film (hereinafter, referred to as a second conductive film) has been used as a data signal line (also referred to as a source wiring). The scan signal line is provided in a horizontal direction with respect to the substrate surface and the data signal line is provided in a vertical direction with respect to the substrate surface.
In a pixel structure of a conventional active matrix display device, an auxiliary capacitor portion which holds a data signal for one frame period (also referred to as an additional capacitor or a storage capacitor) is provided. The auxiliary capacitor portion has employed either a mode in which the first conductive film to be an auxiliary capacitor line and a light-transmitting conductive film to be a pixel electrode formed as an uppermost layer each serve as a capacitor electrode (see Patent Document 1: Japanese Published Patent Application No. H2-48639), or a mode in which the first conductive film to be an auxiliary capacitor line and the second conductive film connected to a light-transmitting conductive film each serve as a capacitor electrode (see Patent Document 2: Japanese Published Patent Application No. H6-202153). The auxiliary capacitor line is provided in parallel to the scan signal line. In either mode, the auxiliary capacitor portion is formed in the same manufacturing process in which formation from an inverted staggered TFT to a pixel electrode is performed, and suppression of increase in the number of steps is a basic purpose of the auxiliary capacitor portion.
A bridge structure is disclosed in which most of a gate wiring and a source wiring which perpendicularly intersect with each other are formed using the first conductive film, and the source wiring which is divided at an intersection of the gate wiring and the source wiring are connected using the second conductive film which crosses the gate wiring (see Patent Document 3: Japanese Published Patent Application No. H1-101519). In addition, a structure is disclosed in which a pixel electrode formed using indium tin oxide (ITO) is formed over a gate insulating film and a counter electrode formed using indium tin oxide (ITO) is formed with a passivation film interposed therebetween to form an auxiliary capacitor portion (See Patent Document 4: Japanese Published Patent Application No. H5-289111).